The long term objectives of this research is to understand the cellular mechanisms by which DNA damage from agents such as ultraviolet irradiation and many carcinogens is processed to give rise to mutations. A considerable amount of the research proposed for the upcoming grant period will focus on defining the genetics and biochemistry of the products of the UmuD and UmuC genes of Escherichia coli. The UmuD and UmuC proteins, as well as their plasmid-coded analogs, MucA and MucB, play a crucial but as yet undetermined role in most chemical and radiation mutagenesis. The UmuD and UmuC proteins will be over-produced, purified, and physically characterized. The biochemical roles of UmuD and UmuC in UV and chemical mutagenesis will be studied and a umuD+ umuC+ dependent in vitro mutagenesis system will be established. The ongoing genetic analysis of the umuDC and mucAB loci will be continued. Other genetic studies of mutagenesis will be initiated in order to investigate such issues as the second role of the RecA protein in mutagenesis. Other organisms will be investigated for the presence of UmuD/UmuC functions. These studies are highly relevant to our understanding of the molecular mechanisms by which chemical carcinogens cause cancer.